In the process of drilling an oil well, it is sometimes necessary to use a drilling mud based on oil rather than water. This oil-based mud wets the well casing and the formation surrounding the well. If the resulting oil film is not removed, the cement which is used to seal the casing to the formation will not adhere to either the casing or the formation.
Chemicals may be pumped into the well to effect removal of the oil film. The chemicals include surfactants in a salt solution. The efficacy of these fluids in removing the oil film may depend on the composition as well as mechanical agitation of the solution. The effectiveness of film removal may be increased by the shearing force resulting from the motion of the clean-up fluid.
The time needed to remove the oil film may depend both on the surfactant formulation and the shear rates generated in the solution. Surfactant solutions must be tested to determine their effectiveness in removing the oil film. Additionally, the efficacy of agitation generated shear forces must also be tested and the application time needed to remove the film determined. Downhole tests require an expensive wireline tool to be implemented at the well. Moreover, currently, no tool exists for making the desired measurements. Together, these make the cost of downhole measurements prohibitive.
Thus, there is a need in the art for an economical apparatus and method for the measurement of the effectiveness of these chemicals in removing an oil film in the presence of shear flows.